Re: [PATCH/RFC 1/2] ALSA: fireface: Fix integer overflow in transmit_midi_msg()

On Mon, 11 Jan 2021 14:02:50 +0100, Geert Uytterhoeven wrote:

As snd_ff.rx_bytes[] is unsigned int, and NSEC_PER_SEC is 1000000000L, the second multiplication in

ff->rx_bytes[port] * 8 * NSEC_PER_SEC / 31250

always overflows on 32-bit platforms, truncating the result. Fix this by precalculating "NSEC_PER_SEC / 31250", which is an integer constant.

Note that this assumes ff->rx_bytes[port] <= 16777.

Fixes: 19174295788de77d ("ALSA: fireface: add transaction support") Signed-off-by: Geert Uytterhoeven geert+renesas@glider.be

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Compile-tested only.

I don't know the maximum transfer length of MIDI, but given it's an old standard, I guess it's rather small. If it is larger than 16777, the constant "8" should be replaced by "8ULL", to force 64-bit arithmetic.

Applied now. Thanks.

Takashi